Technical Field
This disclosure relates to relief valves, and more particularly, to relief valves for use in high pressure and ultrahigh pressure fluid pumps suitable for supplying pressurized fluid for fluid jet cutting and other activities.
Description of the Related Art
Numerous tasks, for example, cutting sheet metal or abrading a surface, may be accomplished through the use of a stream of pressurized fluid, typically water, which is generated by high pressure or ultrahigh pressure, positive displacement pumps, including, for example, those capable of generating pressurized fluid up to and beyond 87,000 psi and including over 100,000 psi. Such pumps pressurize a fluid by having a reciprocating plunger that draws the fluid from an inlet area into a pressurization chamber during an intake stroke, and acts against the fluid during a pumping stroke, thereby forcing pressurized fluid to pass from the pressurization chamber to an outlet chamber where it is collected to be used by an operator via whatever tool has been attached to the pump for a particular task.
During the normal course of operation, the required flow rate will vary from the maximum the pump can supply to zero, for example, when the operator turns the tool off. In this situation, where the pressurized fluid is not being used, the pressure in the outlet chamber will build up beyond an acceptable level unless some form of pressure control is incorporated into the pump. If no pressure control is provided, the buildup of pressure will result in damage and stress to the parts of the pump and undesirable surges of pressure will occur when the operator again turns the tool on.
One method of pressure control that is currently used is to incorporate a relief valve into the pump. When the pressure in the outlet chamber rises above a preset limit as a result of pressurizing more water than is demanded, the relief valve opens to vent the excess pressurized fluid. A relief valve may be direct acting, meaning that pressurized fluid acts directly to open a poppet that is being held in a closed position by a control force, such as, for example a spring or other biasing mechanism. Example relief valves are shown and described in U.S. Pat. No. 5,564,469, which is incorporated herein by reference in its entirety, and which is assigned to the assignee of the present application, Flow International Corporation of Kent, Wash. While currently available direct acting relief valves for high pressure and ultrahigh pressure pumps provide suitable relief under many operating conditions, in some instances, a pressure signal corresponding to the system pressure can oscillate unsatisfactorily above and below a desired pressure due to variations in the hydrostatic and hydrodynamic forces acting on the relief valve during operation. Applicants believe improved relief valves less susceptible to pressure oscillations are desirable.